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Are you able to sign in using Safe Boot mode?
Restart your Mac
As soon as you hear the Startup chime, press and hold the SHIFT key
Continue to hold the Shift key until you see the Apple logo and progress indicator.
Then, let go of the Shift key and let it boot to the login screen (it may take longer than usual so please be patient).
If you can sign in, restart and verify whether it still works or not and then let me know.